Patent Literature 1 discloses an invention relating to a laminated film including a metal layer and a polyimide resin layer, the laminated film being used for a fixing film for use in an image-heating apparatus for heat-fixing an unfixed image. Here, the polyimide resin layer is used to reduce the frictional resistance between the fixing film and a film-guiding member which is arranged on the backside of the fixing film and which is in contact with the back surface of the fixing film in a fixing device. Patent Literature 1 discloses that an imidization rate of the polyimide resin layer of 75% to 93% results in improvement in the flexibility of the polyimide resin layer, thereby relieving mechanical stress on the metal layer and improving the durability of the entire laminated film.